Rich Communication Service (RCS) is a communication protocol that supports Internet Protocol (IP)-based communication between end devices and across different mobile telephone service providers. Envisioned as a replacement for legacy short message service (SMS) messages and an alternative to third-party over-the-top OTT messaging applications, RCS provides a communication system that, in addition to text-based messages, also supports IP voice and video calls, group chats, file transfers, etc. Designing an RCS system to be cross-platform and carrier agnostic, and that facilitates efficient and secure handling of communications between customers of different service providers has proven challenging.